A direct-methanol fuel cell comprises an anode into which an aqueous methanol solution is introduced as fuel, a cathode into which an oxidizing gas is introduced, an electrolyte membrane interposed between these electrodes, a fuel separator which is disposed in the anode and comprises a fuel passage, and a cathode separator which is disposed in the cathode and comprises an oxidizing gas passage. As each of these separators, a carbon plate or SUS plate is currently used.
In such a direct-methanol fuel cell, droplets of water-methanol condense primarily on the inside surface of the oxidizing gas passage of the cathode separator in the process of generating electricity. The droplets of liquid clog the oxidizing gas passage, that is, cause so-called flooding, which hinders the flow of the oxidizing gas such as air. As a result, the reduction reaction of the cathode is hindered, degrading the output and reliability of the fuel cell.